The popularity of cordless portable devices, such as power tools, has increased the needs and requirements for high energy density rechargeable batteries that can also deliver high power. As power and energy density requirements increase, the need for a high cycle life rechargeable electrode also increases. The alkaline zinc electrode is known for its high voltage, low equivalent weight and low cost. The fast electrochemical kinetics associated with the charge and discharge process enables the zinc electrode to deliver both high power and high energy density.
The low redox potential associated with zinc renders the electrode unstable with respect to hydrogen evolution. Primary alkaline batteries that employ zinc have dealt with this problem by alloying zinc with specific elements and using gassing inhibitors. The purity of materials coming in contact with zinc is important, as well as limiting the exposure of zinc to any hydrogen evolution catalyst. The differences between the starting materials for the primary and rechargeable cell affect the techniques and the effectiveness of any corrosion inhibition approach. Zinc primary batteries are manufactured in a charged state while zinc secondary batteries are manufactured in a largely discharged state. In zinc primary batteries, the active material is metallic zinc in a gelled powder form with particles between 100 to 300 microns. In zinc secondary batteries, the active material is zinc oxide (ZnO), with small amounts of zinc metal, with particle size on the order of 0.2 to 0.3 microns. The small zinc oxide particle size used in the negative electrode of rechargeable cells results in a surface area that is 2 orders of magnitude larger than the particles in zinc electrodes used in primary batteries. The corrosion rate of zinc is significantly higher in a secondary battery, once it is formed after the initial charge. Improvements in rechargeable zinc electrode composition and manufacturing technique to minimize corrosion and improve manufacturability continue to be sought.